Discussion on Condition-Based Maintenance of Relay Protection Devices

   Relay protection devices play an important role in the power system, and their normal operation will have a significant impact on the operation of the power system. How to improve the reliability of relay protection devices has become an increasingly important topic of concern. Therefore, it is necessary to sort out and analyze the "condition-based maintenance" of the power system, hoping to be helpful for future work.Line power frequency parameter tester integratesheterogeneous frequency test power supply, measuring instruments, and mathematical models into one, eliminating the influence of strong interference, ensuring the safety of equipment, and can measure the power frequency parameters of transmission lines extremely conveniently, quickly, and accurately.

    1. Overview of Condition-Based Maintenance

    Condition-based maintenance, also called predictive maintenance, as the name implies, is to determine whether to maintain equipment based on the quality of its operating status. Condition-based maintenance is a preventive operation based on the condition of the equipment. Condition-based maintenance was first proposed by DuPont in the United States. It takes the current working condition of the equipment as the basis for maintenance, diagnoses the health status of the equipment through condition monitoring means, and determines whether the equipment needs maintenance or the timing of maintenance. The goal of condition-based maintenance is to reduce equipment downtime, improve equipment reliability and availability factor, extend equipment life, reduce operation and maintenance costs, improve equipment operating performance, and increase economic benefits.

    Relay protection devices refer to an automation measure and equipment that, when power components in the power system (such as generators, lines, etc.) or the power system itself fail or events endanger its safe operation, promptly send warning signals to the operating duty personnel, or directly issue trip commands to the controlled switches to terminate the development of these events. Power equipment safety is an eternal theme of the power system. As the power grid develops increasingly large, users have higher and higher requirements for power reliability. For traditional relay protection devices, they do not provide self-check or condition monitoring functions, so strict periodic maintenance is required to discover potential defects or faults in protection devices and reduce the probability of misoperation or refusal. Under the condition that its components have been selected, the improvement of reliability largely depends on the determination of the maintenance cycle. If maintenance is performed regardless of the equipment's condition, as long as the time is due, it not only increases the labor intensity on site but also may not be beneficial to the health of the equipment, the reliability of power supply, and the safety of personnel. Condition-based maintenance is based on effective monitoring of equipment condition, arranging maintenance time and items according to the results of monitoring, analysis, and diagnosis. It mainly includes three links: equipment condition monitoring, equipment diagnosis, and maintenance decision-making. Condition monitoring is the basis of condition-based maintenance, condition monitoring is the basis of equipment diagnosis, and maintenance decision-making is to determine specific maintenance plans or strategies by combining online monitoring and diagnosis with the technical application requirements of equipment and systems. Therefore, implementing condition-based maintenance will become an inevitable choice for protecting relay equipment.

   2. Identification of the "Condition" of Relay Protection Devices

   1. Pay attention to a comprehensive understanding of the initial state of the equipment

   The initial state of the equipment has a decisive impact on its future safe operation. A good initial state of the equipment is the key to reducing the workload of equipment maintenance and is also a key link in condition-based maintenance work. Attention should be paid to the processing and organization of equipment original records, equipment ledgers, drawings, technical materials, and relevant equipment operation, maintenance, and test data. Therefore, to implement condition-based maintenance, the basic management of equipment must first be done well. An important foundation for the implementation of condition-based maintenance of relay protection equipment is that there should be no blind spots in the collection of equipment condition characteristic quantities. Condition-based maintenance is not just the work of the maintenance link, but the management of the entire process that must be paid attention to in all links of the equipment's entire life cycle. There are two aspects of work that need special attention. On the one hand, it is to ensure that the equipment is in a healthy state initially and should not have inherent deficiencies before being put into operation. Condition-based maintenance, as a decision-making technology for equipment maintenance, aims to determine the appropriate timing for maintenance. On the other hand, before the equipment is put into operation, there should be a relatively clear understanding of the equipment, and as much 'fingerprint' information as possible should be mastered. This includes the equipment's nameplate data, type test and special test data, factory test data, factory test data of each component, handover test data, and construction records.

   2. Pay attention to the statistical analysis of equipment operating status data

   To implement condition-based maintenance, accurate data that can describe the equipment condition must be available. That is to say, a large amount of effective information is needed for analysis and decision-making. Equipment components under load and environmental conditions produce wear, corrosion, stress, creep, fatigue, and aging, etc. Failure causes equipment damage and stops operation. These damages develop gradually and generally have certain laws. Under different conditions, some are changes in physical quantities, some are changes in chemical quantities, some are changes in electrical parameters. In addition, there are equipment operating time, start-stop times, load changes, limit-exceeding data and time, environmental conditions, etc. Therefore, it is necessary to strengthen the data analysis of the historical operating status of relay protection devices. The concept of modern data comprehensive management is the organic combination of databases and analysis systems. The foundation of condition-based maintenance data management is a series of databases, including operation records, design data, maintenance history records, equipment condition monitoring and diagnosis data, unit performance analysis data, etc. Correct and complete technical data is the basis of condition-based maintenance. Condition monitoring of relay equipment will help to achieve effective management and information sharing of equipment operation conditions, defect and fault conditions, and previous maintenance and test records, and provide a reliable information basis for the analysis of equipment operating conditions. It will help to reasonably formulate equipment maintenance strategies, improve the availability of protection devices, and is very important for ensuring the safety of systems and equipment.

   3. Apply new technologies to monitor and test equipment

   To carry out condition-based maintenance work, it is inevitable to adopt new technologies extensively. Under the current situation where online monitoring technology is not mature enough to meet the needs of condition-based maintenance, only by combining online data with offline data and conducting multi-factor comprehensive analysis and evaluation can more accurate and credible conclusions be obtained. A certain power supply bureau installed HYDRAN201R intelligent online transformer early fault monitoring devices produced by YPROTEC of Canada on all 26 500kV and 220kV main transformers, establishing an early fault monitoring system for large-capacity main transformers in the Dalian power grid, with good results. In addition, mature offline monitoring devices and technologies can be fully utilized, such as infrared thermal imaging technology, transformer winding deformation testing, etc., to test equipment in order to analyze the condition of the equipment and ensure the safety of equipment and systems.

   3. Issues to Pay Attention to in Carrying Out Condition-Based Maintenance of Relay Protection

   1. Strictly follow the principles of condition-based maintenance

   The implementation of condition-based maintenance should follow the following principles: First, ensure the safe operation of equipment. In the process of implementing equipment condition-based maintenance, take ensuring the safe operation of equipment as the primary principle, strengthen the monitoring and analysis of equipment condition, scientifically and reasonably adjust maintenance intervals and maintenance items, and formulate corresponding management systems. Second, overall planning, step-by-step implementation, pilot first, and gradual promotion. Implementing equipment condition-based maintenance is a reform of the current maintenance management system and is a complex systematic project. Since China is still in the exploration stage, the implementation of equipment condition-based maintenance should have both long-term goals and overall concepts, and also be solid and steady, step-by-step implementation, and gradually promote on the basis of successful pilot experience. The implementation of condition-based maintenance can start with the implementation of equipment spot inspection and fixed maintenance system and standardization and normalization of maintenance operations, fully implement the responsibility system for equipment management, standardize and improve the basic management of maintenance, strengthen the quality management of maintenance, improve the health level of equipment, and keep the equipment in a good state. In this way, a good foundation can be laid for the comprehensive implementation of equipment condition-based maintenance from the aspects of ideology, system, personnel, and technology. During the implementation process, attention should also be paid to timely summarizing experience and adjusting plans if necessary. Third, fully utilize existing technical means and appropriately configure monitoring equipment.

   2. Pay attention to the technical management requirements of condition-based maintenance

   Condition-based maintenance needs scientific management to support it. Relay protection devices are usually static in the power system, but in the power system, what needs to be understood is precisely whether the relay protection device can act quickly and accurately when a power system fault occurs, that is, to grasp the dynamic "condition" of the relay protection device. Therefore, it is obviously inappropriate to judge its dynamic characteristics based on the understanding of the static characteristics of the relay protection device. Therefore, by simulating the parameters felt by the relay protection device under power accidents and abnormal conditions, the relay protection device is started and acted, and the logical functions and action characteristics that the relay protection device should have are checked, thereby understanding and grasping the condition of the relay protection device. This kind of inspection of relay protection devices is very necessary and essential for the power system.
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